The present invention generally relates to a semiconductor device in which a metal wiring is formed so as to be electrically connected to an electrode of a semiconductor element and a part of the metal wiring is used as an external electrode, and a manufacturing method of the same. More particularly, the present invention relates to a semiconductor device having excellent junction reliability between a metal wiring and a ball electrode mounted to an external electrode portion of the metal wiring, and a manufacturing method of the same.
With recent reduction in size and improvement in functions of electronic equipments, an increasing number of input/output (I/O) pins is formed in a semiconductor element, and therefore the pitch of electrodes is reduced.
Especially in a CSP (Chip Size Package) type semiconductor device, electrodes of a semiconductor element are formed by a dry etching method in a diffusion process, whereas wiring electrodes of a substrate on which the semiconductor element is mounted are formed by a wet etching method in an assembling process. Accordingly, the pitch of the wiring electrodes of the substrate on which the semiconductor element is mounted is necessarily greater than that of the electrodes of the semiconductor element. In view of this, a semiconductor device is increasingly developed which deals with the difference between the electrode pitch of the semiconductor element and the wiring-electrode pitch of the substrate. In such a semiconductor device, metal wirings are formed so as to be electrically connected to the respective electrodes of the semiconductor element and a part of each metal wiring is used as an external electrode in order to increase the distance between the external electrodes.
Hereinafter, a conventional semiconductor device will be described with reference to the figures.
FIG. 15A is a perspective plan view of the conventional semiconductor device. FIG. 15B shows an example of the cross-sectional structure taken along line XVxe2x80x94XV of FIG. 15A. FIG. 15C shows another example of the cross-sectional structure taken along line XVxe2x80x94XV of FIG. 15A.
As shown in FIGS. 15A and 15B, electrodes 2 are formed on the surface of a semiconductor element 1. A passivation film 3 is formed over the surface of the semiconductor element 1. The passivation film 3 is formed from silicon nitride (SiN) or the like, and has an opening on each electrode 2. Metal wirings 4 are formed on the passivation film 3. Each metal wiring 4 is formed from copper (Cu) and electrically connected to a corresponding one of the electrodes 2. A solder resist film 5 is formed on the metal wirings 4 and the passivation film 3. The solder resist film 5 has an opening on a portion of each metal wiring 4 which functions as an external electrode (hereinafter, referred to as xe2x80x9cexternal electrode portionxe2x80x9d). In order to electrically connect the electrodes 2 formed on the surface of the semiconductor element 1 to wiring electrodes of a substrate (not shown) on which the semiconductor element 1 is mounted, respectively, a ball electrode 6 formed from solder is connected in a molten state to each opening of the solder resist film 3, that is, to the external electrode portion of each metal wiring 4.
As shown in FIG. 15C, an insulating resin layer 7 may be formed between the semiconductor element 1 having the passivation film 3 thereon and the metal wirings 4.
In each of the forms of the conventional semiconductor device described above, the wiring electrodes of the substrate on which the semiconductor device is mounted are respectively connected to the metal wirings 4 of Cu formed on the surface of the semiconductor element 1 through the ball electrodes 6 formed from solder. In other words, when the metal wirings 4 are formed from Cu (which is a commonly used metal wiring material), metal junction of Cu (the metal wirings 4) and solder (the ball electrodes 6) is formed at the boundary between the metal wiring 4 and the ball electrode 6.
In the above conventional semiconductor device, however, tin (Sn) contained in solder of the ball electrode 6 diffuses into Cu of the metal wiring 4 to form a Snxe2x80x94Cu alloy layer. As a result, in the portion of the metal wiring 4 on which the ball electrode 6 is mounted (i.e., the external electrode portion) and the portion near the external electrode portion, the Snxe2x80x94Cu alloy grows in the most part of the metal wiring 4. The Snxe2x80x94Cu alloy is weak and hard. The semiconductor device 1, the resin film covering the surface of the semiconductor element 1 and the substrate have different thermal expansion coefficients. Accordingly, when the temperature is varied to melt the ball electrodes in the process of mounting the semiconductor device onto the substrate, stresses are generated due to such a difference in thermal expansion coefficient. Accordingly, the Cuxe2x80x94Sn alloy layer formed in the portion of the metal wiring 4 to which the ball electrode 6 is mounted is likely to be broken by the stresses.
In view of the above problems, it is an object of the present invention to provide a semiconductor device having a metal wiring electrically connected to an electrode of a semiconductor element, and having improved junction reliability between the metal wiring and a ball electrode mounted on an external electrode portion of the metal wiring.
According to one aspect of the present invention, a semiconductor device includes a semiconductor element having an electrode formed on a surface thereof, and a metal wiring formed on the surface of the semiconductor element and electrically connected to the electrode. The metal wiring has an external electrode portion functioning as an external electrode. A thickness of the external electrode portion is greater than that of a non-electrode portion of the metal wiring, i.e., a portion of the metal wiring other than the external electrode portion.
According to the above semiconductor device, in the metal wiring electrically connected to the electrode of the semiconductor element, the thickness of the external electrode portion is greater than that of the non-electrode portion. The external electrode portion of the metal wiring and a wiring electrode of a substrate on which the semiconductor device is mounted may be connected to each other by a ball electrode formed from solder. In this case, when the metal wiring contain, e.g., Cu (which is a commonly used metal wiring material), Sn contained in solder of the ball electrode diffuses into Cu contained in the metal wiring, whereby a Snxe2x80x94Cu alloy layer having low strength grows in the thickness direction of the external electrode portion. However, since the thickness of the external electrode portion of the metal wiring is greater than that of the non-electrode portion of the metal wiring, this Snxe2x80x94Cu alloy layer can be prevented from growing through the entire thickness of the external electrode portion. In other words, it is ensured that the thickness of the low-strength Snxe2x80x94Cu alloy layer in the external electrode portion of the metal wiring is smaller than the thickness of the external electrode portion. Since a part of the external electrode portion is left unchanged into the Snxe2x80x94Cu alloy layer, the strength of the metal wiring can be maintained even if Cu is used as a metal wiring material. The semiconductor element, the resin film covering the surface of the semiconductor element, and the substrate have different thermal expansion coefficients. Therefore, when the temperature is varied in the process of hardening the resin film covering the surface of the semiconductor element or the process of mounting the semiconductor device onto the substrate, stresses are generated due to such a difference in thermal expansion coefficient. However, the above structure can prevent disconnection of the metal wiring even if such stresses are generated.
According to the above semiconductor device, the thickness of the non-electrode portion of the metal wiring is smaller than that of the external electrode portion to which the ball electrode is mounted. The metal wiring having a small thickness facilitates formation of fine wirings by etching. As a result, the width of the metal wiring or the pitch of the metal wirings can be reduced, enabling reduction in size of the semiconductor device.
Preferably, the semiconductor device further includes an insulating film formed on the metal wiring and the surface of the semiconductor element, and having an opening exposing the external electrode portion. An exposed surface of the external electrode portion is preferably flush with or higher than a surface of the insulating film.
This prevents a wiring or electrode of a substrate on which the semiconductor device is mounted from contacting the non-electrode portion of the metal wiring of the semiconductor device. Moreover, the exposed surface of the external electrode portion is flush with or higher than the surface of the insulating film. Therefore, the ball electrode can be mounted to the external electrode portion without producing a gap therebetween. As a result, sufficient junction between the ball electrode and the external electrode portion can be ensured. When the exposed surface of the external electrode portion is higher than the surface of the insulating film, a substantial thickness of a metal portion of the external electrode portion is increased. Therefore, the following effects can be obtained: when Sn contained in solder of the ball electrode diffuses into Cu contained in the metal wiring, a Snxe2x80x94Cu alloy layer having low strength grows in the thickness direction of the external electrode portion. As described above, however, since the substantial thickness of the metal portion of the external electrode portion is increased, it is ensured that a greater part of the external electrode portion is left unchanged into the Snxe2x80x94Cu alloy in the thickness direction of the external electrode portion. When the temperature is varied in a process such as the process of mounting the semiconductor device onto the substrate, stresses are generated due to the difference in thermal expansion coefficient between the semiconductor device and the substrate. However, the above structure can more reliably prevent disconnection of the metal wiring even if such stresses are generated. Note that, when the exposed surface of the external electrode portion is higher than the surface of the insulating film, the external electrode portion may be bonded to the wiring electrode of the substrate by solder without using the ball electrode. In this case, the same effects as those described above can be obtained.
Preferably, the metal wiring is formed from a metal containing copper.
This enables reduction in resistance of the metal wiring.
Preferably, the above semiconductor device further includes an insulating resin layer formed between the surface of the semiconductor element and the metal wiring. The metal wiring is preferably formed along a surface of the insulating resin layer.
When the temperature is varied to melt the ball electrode in the process of mounting the semiconductor device to the substrate, stresses are generated due to the difference in thermal expansion coefficient between the semiconductor device and the substrate. However, these stresses can be absorbed by the insulating resin layer. As a result, the stresses are reduced, whereby the external electrode portion of the metal wiring to which the ball electrode is connected can be prevented from being broken by the stresses.
Preferably, the thickness of the external electrode portion is in a range of 10 xcexcm to 20 xcexcm.
In this case, the metal wiring can be reliably prevented from being disconnected at the external electrode portion, and pattern deformation generated in the process of forming the external electrode portion having a greater thickness by etching can be suppressed.
According to another aspect of the present invention, a method for manufacturing a semiconductor device includes: a first step of forming, on a surface of a semiconductor element having an electrode formed thereon, a metal wiring electrically connected to the electrode; a second step of forming, on the surface of the semiconductor element and the metal wiring, an insulating film having an opening which exposes a region of the metal wiring layer where an external electrode is to be formed; and a third step of forming a metal-material embedded portion in the opening so that a surface of the metal-material embedded portion is flush with or higher than a surface of the insulating film.
According to the above manufacturing method, the metal wiring is formed so as to be electrically connected to the electrode of the semiconductor element. The insulating film is then formed so as to have an opening which exposes the region of the metal wiring where an external electrode is to be formed. Thereafter, the metal-material embedded portion is embedded in the opening so that the surface of the metal-material embedded portion is flush with or higher than the surface of the insulating film. As a result, the thickness of the external electrode portion (i.e., the total thickness of the metal-material embedded portion embedded in the opening and the metal wiring located under the metal-material embedded portion) is greater than the thickness of a non-electrode portion of the metal wiring, that is, the portion of the metal wiring other than the external electrode portion. Accordingly, the same effects as those of the semiconductor device of the present invention can be obtained.
According to the above manufacturing method, the non-electrode portion of the metal wiring (i.e., the portion of the metal wiring other than the external electrode portion) is covered with the insulating film. This prevents a wiring or electrode of a substrate on which the semiconductor device is mounted from contacting the non-electrode portion of the metal wiring of the semiconductor device. Moreover, the surface of the metal-material embedded portion, that is, the exposed surface of the external electrode portion, is flush with or higher than the surface of the insulating film. Therefore, a ball electrode can be mounted to the external electrode portion without producing a gap therebetween. As a result, sufficient junction between the ball electrode and the external electrode portion can be ensured. When the exposed surface of the external electrode portion is higher than the surface of the insulating film, a substantial thickness of a metal portion of the external electrode portion is increased. Therefore, the following effects can be obtained: when Sn contained in solder of the ball electrode diffuses into Cu contained in the metal wiring, a Snxe2x80x94Cu alloy layer having low strength grows in the thickness direction of the external electrode portion. As described above, however, since the substantial thickness of the metal portion of the external electrode portion is increased, it is ensured that a greater part of the external electrode portion is left unchanged into the Snxe2x80x94Cu alloy in the thickness direction of the external electrode portion. When the temperature is varied in a process such as the process of mounting the semiconductor device onto the substrate, stresses are generated due to the difference in thermal expansion coefficient between the semiconductor device and the substrate. However, the above structure can more reliably prevent disconnection of the metal wiring even if such stresses are generated. Note that, when the exposed surface of the external electrode portion (i.e., the surface of the metal-material embedded portion) is higher than the surface of the insulating film, the external electrode portion may be bonded to the wiring electrode of the substrate by solder without using the ball electrode. In this case, the same effects as those described above can be obtained.
Preferably, the above manufacturing method further includes, before the first step, the step of forming an insulating resin film on the surface of the semiconductor element except the electrode. The first step preferably includes the step of forming the metal wiring along a surface of the insulating resin layer.
When the temperature is varied to melt a ball electrode in the process of mounting the semiconductor device to the substrate, stresses are generated due to the difference in thermal expansion coefficient between the semiconductor device and the substrate. According to the above manufacturing method, however, these stresses can be absorbed by the insulating resin layer. As a result, the stresses are reduced, whereby the external electrode portion of the metal wiring to which the ball electrode is connected can be prevented from being broken by the stresses.
In the above manufacturing method, the third step may include the step of forming a metal film on the insulating film so as to completely fill the opening, forming a mask pattern which covers a region of the metal film located on the opening, removing a region of the metal film located outside the mask pattern, and removing the mask pattern.
In the above manufacturing method, the third step may include the step of forming a first metal film on the surface of the insulating film so as to partially fill the opening, forming a mask pattern which covers a region of the first metal film located outside the opening, forming a second metal film on a region of the first metal film located in the opening, and removing the mask pattern and the region of the first metal film located outside the opening.
In the above manufacturing method, the semiconductor element may be provided in each of a plurality of chip regions of a semiconductor wafer, which are defined by a dicing line. The method may further include, after the third step, the step of dicing the semiconductor wafer along the dicing line by a rotating blade in order to divide the semiconductor wafer into chips of the semiconductor elements.
According to still another aspect of the present invention, a method for manufacturing a semiconductor device includes: a first step of forming, on a surface of a semiconductor element having an electrode formed thereon, a metal wiring electrically connected to the electrode; a second step of forming a projecting electrode on a region of the metal wiring where an external electrode is to be formed; and a third step of forming an insulating film on the surface of the semiconductor element and the metal wiring so as to expose at least a top portion of the projecting electrode.
According to the above manufacturing method, the metal wiring is formed so as to be electrically connected to the electrode of the semiconductor element. The projecting electrode is then formed on the region of the metal wiring where an external electrode is to be formed. Thereafter, the insulating film is formed so as to expose at least the top portion of the projecting electrode. As a result, the thickness of the external electrode portion (i.e., the total thickness of the projecting electrode and the metal wiring located thereunder) is greater than the thickness of a non-electrode portion of the metal wiring, that is, the portion of the metal wiring other than the external electrode portion. Accordingly, the same effects as those of the semiconductor device of the present invention can be obtained.
According to the above manufacturing method, the non-electrode portion of the metal wiring (i.e., the portion of the metal wiring other than the external electrode portion) is covered with the insulating film. This prevents a wiring or electrode of a substrate on which the semiconductor device is mounted from contacting the non-electrode portion of the metal wiring of the semiconductor device. Moreover, the surface of the top portion of the projecting electrode, that is, the exposed surface of the external electrode portion, is higher than the surface of the insulating film. Therefore, a ball electrode can be mounted to the external electrode portion without producing a gap therebetween. As a result, sufficient junction between the ball electrode and the external electrode portion can be ensured. Moreover, since the exposed surface of the external electrode portion is higher than the surface of the insulating film, a substantial thickness of a metal portion of the external electrode portion is increased. Therefore, the following effects can be obtained: when Sn contained in solder of the ball electrode diffuses into Cu contained in the metal wiring, a Snxe2x80x94Cu alloy layer having low strength grows in the thickness direction of the external electrode portion. As described above, however, since the substantial thickness of the metal portion of the external electrode portion is increased, it is ensured that a greater part of the external electrode portion is left unchanged into the Snxe2x80x94Cu alloy in the thickness direction of the external electrode portion. When the temperature is varied in a process such as the process of mounting the semiconductor device onto the substrate, stresses are generated due to the difference in thermal expansion coefficient between the semiconductor device and the substrate. However, the above structure can more reliably prevent disconnection of the metal wiring even if such stresses are generated. Note that, when the exposed surface of the external electrode portion (i.e., the top portion of the projecting electrode) is higher than the surface of the insulating film, the external electrode portion may be bonded to the wiring electrode of the substrate by solder without using the ball electrode. In this case, the same effects as those described above can be obtained.
Preferably, the above manufacturing method further includes, before the first step, the step of forming an insulating resin film on the surface of the semiconductor element except the electrode. The first step preferably includes the step of forming the metal wiring along a surface of the insulating resin layer.
When the temperature is varied to melt a ball electrode in the process of mounting the semiconductor device to the substrate, stresses are generated due to the difference in thermal expansion coefficient between the semiconductor device and the substrate. According to the above manufacturing method, however, these stresses can be absorbed by the insulating resin layer. As a result, the stresses are reduced, whereby the external electrode portion of the metal wiring to which the ball electrode is connected can be prevented from being broken by the stresses.
In the above manufacturing method, the semiconductor element may be provided in each of a plurality of chip regions of a semiconductor wafer, which are defined by a dicing line. The above manufacturing method may further includes, after the third step, the step of dicing the semiconductor wafer along the dicing line by a rotating blade in order to divide the semiconductor wafer into chips of the semiconductor elements.